Character recognition apparatus which obtains distance ratios between edges in a character for identification

Abstract

An apparatus for recognizing characters 20 on a document 10 comprises a scanning head 24 and decoding circuits 78, 72, 86, 92, 80, feeding a controller 84. The controller 84 detects the identity of the characters 20A-20N by calculating the ratio found by dividing the time between a first positive pulse 32 and a second positive pulse 34 by the time between the first positive pulse 32 and a last negative pulse 36 and comparing it against a stored table of ratios.

What is claimed is: 
     
       1. An apparatus for identifying a predetermined font character moving relative to a scanning head from among a predetermined set of characters, said apparatus comprising: edge detector means for scanning the character and providing a single analog output signal indicative of the position of the leading and trailing edges in the scanned character;   controller means operative to measure a first distance between the first leading edge and a first selected edge in the scanned character,   also being operative to measure a second distance between the first leading edge and a second selected edge in the scanned character,   controller means operative to measure a first distance between the first leading edge and a first selected edge in the scanned character,   also being operative to measure a second distance between the first leading edge and a second selected edge in the scanned character,   and operative to take the ratio between said first and second distance to create a novel character ratio;   said controller means comprising a stored set of character signals each representative of the expected ratio for a respective one of the characters in said predetermined set of characters;   said controller means being operative to compare the character ratio with each character signal and to provide an indication of the character, from said set, with whose character signals the character ratio matches.   
     
     
       2. An apparatus according to claim 1 wherein said detector means includes a level detector for detecting and providing an output indicative of the polarity of the rate of change of intensity of the scanned character with position; said controller means being operative to select said first and second selected edges on the basis of their respective positions in the sequence of edges and the polarity indication of said output of said level detector. 
     
     
       3. An apparatus according to claim 2 wherein said first selected edge is the next subsequent leading edge, after said first leading edge, and where said level detector provides an output indicative of the same polarity as for said first leading edge; and wherein said second selected edge is the last trailing edge where said level detector provides an output indicative of the opposite polarity to that for said first edge. 
     
     
       4. An apparatus according to claim 3 wherein said predetermined set of characters is the E13B character set. 
     
     
       5. An apparatus according to claim 1 wherein said scanned character is scanned by movement past said edge detector means, said controller means being operative to calculated position in terms of the instant times of passage of edges past the detector means. 
     
     
       6. An apparatus according to claim 1 wherein said scanned character is a magnetic character, and wherein magnetic flux density represents the intensity of the scanned character. 
     
     
       7. An apparatus according to claim 1 wherein the scanned character is optical, and wherein gray level light intensity represents the intensity of the scanned character. 
     
     
       8. An apparatus according to claim 5 wherein said edge detector means includes an edge detector circuit comprising a logic comparator coupled to receive a representation of the instant intensity of the scanned character and further coupled to receive a delayed representation of the instant intensity of the scanned character, and being operative to provide a logical output, indicative by polarity of the sense of the instant difference between said representation of the intensity of the scanned character and said delayed representation of the instant intensity of the scanned character.